The modelled effects of differing fire management strategies on the conifer Callitris verrucosa within semi-arid mallee vegetation in Australia.
Callitris verrucosa is an obligate-seeder co-dominant within flammable semi-arid mallee shrublands in southern Australia. We sought to determine if there is an optimal management solution that provides both a significant reduction in wildfire size and maintains a viable population of C. verrucosa. Using a spatial model, the effects of alternative fire management strategies (pattern and level of controlled burning) on populations of C. verrucosa were simulated. Plant dynamics and fire propagation were simulated in a gridded landscape model (104 cells, c. 1 ha) incorporating topographic variation typical of dune landscapes. Fire propagation was governed by fuel age, and topographic and weather effects, incorporating potential for spot fires and the influence of wind direction. Plant dynamics were determined by known demographic parameters for C. verrucosa. The size of unplanned fires declined significantly as a function of increasing controlled burning level. Mean fire interval was longer at zero or 1% per year of landscape treated with prescribed fire than at higher levels of controlled burning. Mean fire intervals were shorter under the highest probability of unplanned ignition in the flat landscape and in the dune landscape on the slopes. The responses of C. verrucosa populations reflected trends in fire intervals as affected by controlled burning levels/patterns and topography. The lowest population sizes resulted from either high (20% per year) or zero controlled burning. The highest population sizes occurred consistently at an intermediate level of prescribed ignition (5% per year). Population sizes were significantly larger in dune vs. flat landscapes and under random vs. non-random prescribed ignition patterns. Synthesis and applications. The use of prescribed fire to achieve management objectives concerning 'wildfire control' and conservation will involve trade-offs that are affected by landscape characteristics. Prescribed fire is predicted to achieve both a diminution of wildfire size and maintenance of C. verrucosa population in the landscape. The trade-off required to achieve these objectives concerns the appropriate level and pattern of prescribed fire (strategy).